Are you sure you aren't using a singlespeed cog instead of a fixed or track cog?

If you are rolling down the street, the rear wheel is moving.

Is the lockring missing or loose? If so, the cog could be unscrewing itself and that would be disastrous, even deadly.

Oh, you need to take pictures of your bike. Don't post stock photos. Unless you bought the bike that was in that photo. A very important part of being in the BF community is the sharing of lots of pics of your bike.

the chain might be slipping. are you sure you have the right amount of tension? it happened to me when i got a larger cog before i could get a bigger chain, and its obvious that it can happen if the chain is too lose

Chain tension can do that to you. Check that out first, just give the chain a bit of a vertical tap, and if it gives more than a cm or so, move the rear wheel back in the dropouts (or track ends, if Sheldon is actually right) to tighten the chain

the chain might be slipping. are you sure you have the right amount of tension? it happened to me when i got a larger cog before i could get a bigger chain, and its obvious that it can happen if the chain is too lose

Sorry, I ment to say its not moving backward enough to skid, in fact, its not engaging the chain/rear cog. When this problem occurs, my skidding is not even doing a thing to the speed of the bike. I feel like its moving at the same speed.

Even my little tension pushing pedals backward is having a dramatic decrease in speed, whereas this "empty skid" does absolutely nothing to decrease my speed.

PICS. My money is on lockring. If you are still able to pedal your bike forward, then most likely your cog is becoming unscrewed as you pedal backwards due to a missing or loose lockring. Tighten your lockring and post pics of your rear cog/lockring/hub. If your chain is on, and your chainring is tight, the ONLY thing that could be wrong is basically the lockring or some other part of the rear drivetrain

EDIT: Also, usually when you buy a new bike you need to re-tighten the lockring after you ride it a bit

I'm guessing freewheel. If his lockring was a bit loose so that it would allow the cog to unthread a little bit but not all the way, it seems like after just a moment the cog would unscrew enough to engage the lockring and the drivetrain would lock up again. From the sound of the OP, it seems like he's able to coast/backpedal way longer than it would take for the rotation of the wheel to unscrew the cog.

On the other hand, if his cog was unscrewing all the way from the hub, wouldn't he then be unable to pedal the bike after it had screwed all the way off? Granted, I can't say I've experienced either of those conditions because I like to be sure that my equipment is safe to ride on, it just seems like that's what would happen in either case. Correct me if I'm wrong.